JP6331007B2 - Wireless communication system, base station, transmission method, and program - Google Patents

Description

  The present invention relates to a radio communication system, a base station, a transmission method, and a program.

  In the next generation wireless communication system, there is a concern about the depletion of frequency resources as the transmission speed becomes wider and the system diversifies. In recent years, cognitive radio that recognizes the surrounding radio wave environment and the needs of users and autonomously selects and communicates with an optimal frequency and communication system has been studied. In this cognitive radio, dynamic spectrum access in which another radio system secondarily uses a frequency band assigned to an existing radio system has attracted attention from the viewpoint of effective use of frequency resources. Specifically, in the dynamic spectrum access, the second system, which is a new radio system, uses a free spectrum in the frequency band allocated to the first system, which is an existing radio system, so as not to interfere with the communication of the first system. To do.

  FIG. 15 is a configuration diagram of a general communication system for explaining dynamic spectrum access. In the communication system, the second system shares the frequency band assigned to the first system.

  The system shown in FIG. 15 includes a first system base station 1511, a second system first base station 1521, a second system first mobile station 1522, a second system second base station 1531, and a second system second. Mobile station 1532. The second system employs a time division duplex (TDD) method that performs uplink and downlink communications using the same frequency. A protection boundary 1501 of the first system and a base station transmission boundary 1502 of the second system are provided to protect interference from the second system to the first system. The first system protection boundary 1501 indicates an area where the second system can communicate without interfering with the first system, and the second system is not allowed to communicate inside the first system protection boundary 1501.

  In general, the downlink transmission of the base station of the second system has a larger interference with the first system than the uplink transmission of the mobile station of the second system. For this reason, the area where the second system base station can perform downlink transmission is limited. The second system base station transmission boundary 1502 indicates an area where the base station of the second system can perform downlink transmission, and the second system first base station 1521 is disposed inside the second system base station transmission boundary 1502. Downlink transmission is not allowed. On the other hand, since the second system second base station 1531 is arranged outside the base station transmission boundary 1502 of the second system, downlink transmission is permitted. If the second system mobile station is outside the first system protection boundary 1501, uplink communication is permitted.

  As described above, the second system can secondarily use the frequency allocated to the first system without disturbing the communication of the first system.

  FIG. 16 is a configuration diagram for explaining inter-base station interference and inter-mobile station interference in the second system shown in FIG. The second system first base station 1521 is arranged outside the first system protection boundary 1501 and inside the second system base station transmission boundary 1502, and the second system second base station 1531 transmits the base station of the second system. This is an example of arrangement outside the boundary 1502. Here, a solid arrow indicates a desired signal, and a broken arrow indicates an interference signal.

  FIG. 17A shows the radio resources of the cells under the second system first base station 1521, FIG. 17B shows the radio resource usage status of the cells under the second system second base station 1531, The horizontal axis represents time, and the vertical axis represents transmission power. In the state of radio resource use of the cell of the base station 1521 of the second system in FIG. 17A, only the uplink transmission is permitted for the cell of the base station 1521 of the second system, and therefore the t1 and t2 slots that are time slots. , Communication is performed using the uplink. In the radio resource usage status of the cells under the second system second base station 1531 in FIG. 17B, communication is performed using the uplink in the t1 slot and the downlink in the t2 slot. Here, in the t2 slot, since the reverse communication link transmits simultaneously, interference is given from the second system second base station 1531 to the second system first base station 1521. Further, interference is given from the second system first mobile station 1521 to the second system second mobile station 1532. In particular, since the inter-base station interference has a larger coupling gain than the inter-mobile station interference, the problem of interference becomes significant. In the following explanation, only the interference between base stations will be described. Inter-base station interference and mobile station interference are problems inherent to the TDD system.

  As a technique for solving the above problem, a wireless communication system disclosed in Patent Document 1 is known. In Patent Document 1, interference that occurs when transmitting uplink and downlink at the same time between neighboring base stations that employ TDD does not occur by stopping transmission of radio resources with different uplink or downlink. I am doing so. FIG. 18 shows an operation example of Patent Document 1. FIG. 18A shows a cell under the second system first base station 1521 before applying the technique described in Patent Document 1, and FIG. 18B shows a second cell before applying the technique described in Patent Document 1. The radio resource usage status of the cells under the system second base station 1531 is shown. 18C shows a cell under the second system first base station 1521 of the technology of Patent Document 1, and FIG. 18D shows a cell of the second system second base station 1531 of the technology of Patent Document 1. The radio resource usage status of the cell is shown.

  In FIG. 18 (d), in the cell under the second system second base station 1531, by stopping the downlink transmission of the t1 slot having different uplink and downlink between the base stations, the second system first base station 1521 Interference to the cell uplink is reduced. Similarly, Patent Document 1 also suggests a method of reducing interference on the uplink of the cell of the second system first base station 1521 by reducing the transmission power in slots having different uplink and downlink. .

WO2012-165067

  In the technique disclosed in Patent Document 1, transmission signals of radio resources having different uplink and downlink allocations are stopped or transmission power is suppressed. For this reason, the radio communication system disclosed in Patent Document 1 has a problem that radio resources cannot be sufficiently utilized.

  The present invention has been made to solve the above problem, and an object of the present invention is to provide a technique capable of reducing interference between base stations in the second system and improving the throughput of the second system.

  The present invention for solving the above problem is a wireless communication system in which a plurality of base stations use the same frequency, and the first base station on the interfered side and the first base station on the interfered side Measuring means for measuring a channel estimation value between two base stations, multiplication means for multiplying a downlink transmission signal by a transmission weight according to the measured channel estimation value, and the multiplied transmission signal Transmission means for transmitting from the second base station.

  The present invention for solving the above-mentioned problem is a base station of a wireless communication system in which a plurality of base stations use the same frequency, and the first base measured by the first base station on the interfered side A multiplier for multiplying a downlink transmission signal by a transmission weight corresponding to a channel estimation value between the station and the second base station on the interfering side, and transmitting the multiplied transmission signal from the second base station And transmitting means for performing the processing.

  The present invention for solving the above problem is a transmission method of a radio communication system in which a plurality of base stations use the same frequency, and includes a first base station on an interfered side and a second base station on an interfering side A measurement step in which the first base station measures a channel estimation value between, a multiplication step of multiplying a downlink transmission signal by a transmission weight corresponding to the measured channel estimation value, and the multiplied transmission And a transmission step of transmitting a signal from the second base station.

  The present invention for solving the above problem is a program of a base station in a wireless communication system in which a plurality of base stations use the same frequency, and the program designates the base station as a first base station on the interfered side. Multiplying means for multiplying a downlink transmission signal by a transmission weight according to a channel estimation value measured between the first base station and the second base station on the interfering side, and the multiplied transmission It is made to function as a transmission means which transmits a signal from said 2nd base station.

  According to the present invention, it is possible to reduce interference between base stations.

It is a block diagram which shows the structural example of the radio | wireless communications system which concerns on the 1st Embodiment of this invention. 2 is a flowchart of the radio communication system according to the first embodiment of the present invention. It is a block diagram which shows the structural example of the 2nd system 1st base station shown in FIG. It is a block diagram which shows the structural example of the 2nd system 2nd base station shown in FIG. It is a schematic diagram which shows the radio | wireless resource usage condition for demonstrating operation | movement of the radio | wireless communications system which concerns on the 1st Embodiment of this invention. It is a schematic diagram which shows the radio | wireless resource usage condition for demonstrating operation | movement of the radio | wireless communications system which concerns on the 1st Embodiment of this invention. It is a schematic diagram for demonstrating the null steering operation | movement of the radio | wireless communications system which concerns on the 1st Embodiment of this invention. It is a block diagram which shows the structural example of the radio | wireless communications system which concerns on the 2nd Embodiment of this invention. It is a block diagram which shows the structural example of the 2nd system 1st base station shown in FIG. It is a block diagram which shows the structural example of the 2nd system 2nd base station shown in FIG. It is a block diagram which shows the structural example of the radio | wireless communications system 2nd system 2nd base station which concerns on the 3rd Embodiment of this invention. It is a flowchart of the radio | wireless communications system which concerns on the 2nd Embodiment of this invention. It is a schematic diagram which shows the radio | wireless resource usage condition for demonstrating operation | movement of the radio | wireless communications system which concerns on the 3rd Embodiment of this invention. It is a schematic diagram for demonstrating the null steering and beam forming operation | movement of the radio | wireless communications system which concerns on the 3rd Embodiment of this invention. It is a schematic diagram for demonstrating the communication link of the 2nd system at the time of frequency sharing. It is a schematic diagram for demonstrating the interference between 2nd systems at the time of frequency sharing in a TDD system. It is a schematic diagram which shows the radio | wireless resource usage condition for demonstrating the interference between 2nd systems at the time of frequency sharing in a TDD system. 10 is a schematic diagram showing a radio resource usage situation of a conventional radio communication system disclosed in Patent Document 1. FIG.

  In each embodiment of the present invention described below, a frequency sharing type radio communication system equipped with a plurality of antennas adopting a TDD scheme as a duplex scheme will be described as an example.

[First Embodiment]
FIG. 1 is a configuration diagram for explaining a radio communication system according to the first embodiment of the present invention. The wireless communication system of the present invention is composed of a first system and a second system. The first system is an existing wireless communication system, and a single antenna base station 111 is illustrated. The second system is a cognitive radio communication system that can secondarily use the frequency band assigned to the first system. The second system includes a second system first base station 121 having a plurality of antennas, a second system first mobile station 122, a second system second base station 131 having a plurality of antennas, and a second system second mobile station. 132. The second system first base station 121 is arranged near the first system radio 111 and has a second system first mobile station 122 under the control. The second system second base station 131 is disposed far from the first system radio 111, and has a second system second mobile station 132 under its control. The second system first base station 121 and the second system second base station 131 are connected via an inter-base station interface 141. In this wireless communication system, the area in which the second system base station can perform downlink transmission is limited, and the second system first base station 121 is located inside the transmission boundary of the second system base station. However, uplink transmission is permitted, but downlink transmission is not permitted. On the other hand, since the second system second base station 131 is disposed outside the base station transmission boundary of the second system, uplink and downlink transmission are permitted in the subordinate cell. The first mobile station 122 and the second mobile station 132 of the second system are allowed to perform uplink communication outside the first system protection boundary.

  FIG. 2 is a flowchart showing an operation example of a null steering operation in which the second system second base station 131 on the interfering side reduces interference with the second system first base station 121 on the interfered side.

  The second system second base station 131 performs downlink transmission to the second system second mobile station 132 (step A01).

  The second system first base station 121 receives, for example, a pilot signal transmitted from the second system second base station 131, and performs channel estimation between the second system second base station 131 and the first base station 121. Measure the value. The channel estimation value can be obtained, for example, by correlation processing between the pilot replica and the received pilot signal (step A02).

  The second system first base station 121 notifies the acquired channel estimation value to the second system second base station 131 via the inter-base station interface 141 (step A03).

  The second system second base station 131 applies null steering to reduce the interference to the second system first base station 121 using the channel estimation value notified via the inter-base station interface 141, and then downloads Transmit (step A04).

  FIG. 3 is a block diagram illustrating a configuration of the second system first base station 121 in the wireless communication system according to the first embodiment of the present invention. The second system first base station 121 receives the pilot signal of the radio signal transmitted from the second system second base station 131, and sends the channel estimation value to the second system second base station via the inter-base station interface 141. 131 is notified. Second system first base station 121 includes a channel estimation value measurement unit 301 and a channel estimation value 302.

  The channel estimation value measurement unit 301 receives, for example, a pilot signal of wireless communication transmitted from the second system second base station 131, and performs second processing second base station 131 and second system first base station 121 by correlation processing. Measure the channel estimate between. The channel estimation value is preferably a vector composed of complex numbers corresponding to the number of antennas. Channel estimation value measurement section 301 outputs the measured channel estimation value to channel estimation value notification section 302.

  The channel estimation value notification unit 302 receives the channel estimation value measured from the channel estimation value measurement unit 301 and notifies the second system second base station 131 via the inter-base station interface 141.

  FIG. 4 is a block diagram showing a configuration of the second base station 131 in the second system of the wireless communication system according to the first embodiment of the present invention. The second system second base station 131 acquires a channel estimation value notified from the second system first base station 121 via the inter-base station interface 141, applies null steering, and transmits the downlink channel estimation value.

  Second system second base station 131 includes a channel estimation value acquisition unit 401, a null steering weight generation unit 402, a downlink transmission signal generation unit 403, a multiplication unit 404, and an RF (Radio Frequency) transmission unit 405. .

  The channel estimation value acquisition unit 401 acquires a channel estimation value from the second system first base station 121 via the inter-base station interface 141. Channel estimation value acquisition section 401 outputs the acquired channel estimation value to null steering weight generation section 402.

  The null steering weight generation unit 402 receives the channel estimation value from the channel estimation value acquisition unit 401 and null steering weight so that interference from the second system second base station 131 to the second system first base station 121 is reduced. Is generated. The null steering weight can be obtained by a zero forcing algorithm, for example, and is preferably a vector composed of complex numbers corresponding to the number of antennas. The null steering weight generation unit 402 outputs the generated null steering weight to the multiplication unit 404.

  Downlink transmission signal generation section 403 generates a downlink baseband signal composed of transmission data, a control signal, and a pilot signal, and outputs it to multiplication section 404.

  Multiplier 404 receives the null steering weight from null steering weight generator 402, receives the downlink baseband signal from downlink transmission signal generator 403, and linearly multiplies the downlink baseband signal with the null steering weight. Multiplier 404 outputs the downlink baseband signal obtained by linear multiplication to RF transmitter 405.

  The RF transmission unit 405 inputs the downlink baseband signal after linear multiplication from the multiplication unit 404, and converts the downlink baseband signal after linear multiplication into a high-frequency radio frequency transmitted from the antenna.

  FIG. 5 is a schematic diagram showing a usage state of radio resources at a used frequency when steps A01 and A02 in the flowchart of FIG. 2 are executed. FIG. 5A shows radio resources of cells under the second system first base station 121, FIG. 5B shows radio resources of cells under the second system second base station 131, and the horizontal axis Represents time, and the vertical axis represents transmission power.

  5 (a) In the cell under the second system first base station 121, uplink transmission is performed in the t1 slot, and the channel estimation value between the base stations is measured in the t2 slot. In the cell under the second system second base station 131 in FIG. 5B, uplink transmission is performed in the t1 slot, and downlink transmission is performed in the t2 slot.

  FIG. 6 is a schematic diagram showing a use state of radio resources at a use frequency at the time of execution of step A04 in the flowchart of FIG. In the cell under the control of the second system first base station 121 in FIG. 6A, uplink transmission is performed in the t1 and t2 slots. In the cell under the control of the second system second base station 131 in FIG. 6B, uplink transmission is performed in the t1 slot, and downlink transmission is applied in the t2 slot by applying null steering.

  FIG. 7 is a schematic diagram showing inter-base station interference when step A04 in the flowchart of FIG. 2 is executed. In the first embodiment, null steering is applied so that the directivity of the transmission beam is not directed to the second system first base station 121 in the second system second base station 131 in the t2 slot.

  With the above configuration and operation, in the first embodiment of the present invention, the channel estimation value between the base stations is fed back and null-steered to stop the transmission signal or suppress the transmission power between the base stations. Interference can be reduced.

[Second Embodiment]
The second embodiment is an example in which PMI (Precoding Matrix Indicator) is fed back from the second system first base station 121 to the second system second base station 131. Hereinafter, only the differences from the first embodiment will be described in the description of the second embodiment.

  FIG. 8 is a configuration diagram showing a radio communication system according to the second embodiment of the present invention. In FIG. 8, the PMI is notified from the second system first base station 121 to the second system second base station 131 via the inter-base station interface 141 instead of the channel estimation value.

  FIG. 9 is a block diagram showing a configuration of the second system first base station 121 in the radio communication system according to the second embodiment of the present invention. Second system first base station 121 includes channel estimation value measuring section 401, codebook holding section 901, PMI selecting section 902, and PMI notifying section 903.

  Channel estimation value measurement section 301 outputs the measured channel estimation value to PMI selection section 902.

  The code book holding unit 901 holds a code book that is a weight (precoding) candidate for performing a predetermined null steering operation. The code book holding unit 901 outputs the held code book to the PMI selection unit 902.

  PMI selection section 902 receives a channel estimation value from channel estimation value measurement section 301, receives a codebook from codebook holding section 901, and selects a PMI that is a precoding index that reduces interference between base stations. . The PMI selection unit 902 outputs the selected PMI to the PMI notification unit 903.

  The PMI notification unit 903 inputs the PMI from the PMI selection unit 902 and notifies the input PMI to the second system second base station 131 via the inter-base station interface 141.

  FIG. 10 is a block diagram showing a configuration of the second system second base station 131 of the radio communication system according to the second embodiment of the present invention. The second system second base station 131 includes a PMI acquisition unit 1001, a codebook holding unit 901, a null steering weight generation unit 1002, a downlink transmission signal generation unit 403, a multiplication unit 404, and an RF transmission unit 405. Including.

  The PMI acquisition unit 1001 receives the PMI notified from the second system first base station 121 via the inter-base station interface 141, and outputs it to the null steering weight generation unit 1002.

  The code book holding unit 901 holds a code book that is a predetermined precoding weight candidate for performing a null steering operation. The code book holding unit outputs the held code book to the null steering weight generation unit 1002.

  The null steering weight generation unit 1002 receives the PMI from the PMI acquisition unit 1001, inputs the codebook from the codebook holding unit 901, and acquires the precoding weight corresponding to the PMI from the codebook, thereby obtaining the null steering weight. Is generated. The null steering weight generation unit 1002 outputs the generated null steering weight to the multiplication unit 404.

  With the above configuration and operation, the second embodiment of the present invention reduces the amount of information fed back between base stations by feeding back quantized PMI instead of channel estimation values between base stations. Inter-base station interference can be reduced.

[Third Embodiment]
The third embodiment is an example in which null steering and beam forming are used in combination. Hereinafter, in the description of the third embodiment, only differences from the first embodiment will be described.

  FIG. 11 is a block diagram showing a configuration of a second base station 131 in the second system of the radio communication system according to the third embodiment of the present invention. Second system second base station 131 includes channel estimation value acquisition section 1101, null steering weight generation section 1102, channel estimation value measurement section 1103, beamforming weight generation section 1104, weight combining section 1105, and downlink transmission. A signal generation unit 403, a multiplication unit 404, and an RF transmission unit 405 are included.

  Channel estimation value acquisition section 1101 acquires a channel estimation value from second system first base station 121 via inter-base station interface 141. Channel estimation value acquisition section 1101 outputs the acquired channel estimation value to null steering weight generation section 1102 as the first channel estimation value.

  The null steering weight generation unit 1102 receives the first channel estimation value from the channel estimation value acquisition unit 1101, generates a null steering weight as in the first embodiment, and outputs the null steering weight to the weight synthesis unit 1105.

  The channel estimation value measuring unit 1103 receives, for example, a pilot signal of a radio signal transmitted from the second system second mobile station 132 that is a desired terminal of the second system second base station 131, and performs second processing by the correlation processing. The channel estimation value between the two mobile stations 132 and the second system second base station 131 is measured. Channel estimation value measurement section 1103 outputs the measured channel estimation value to beamforming weight generation section 1104 as the second channel estimation value.

  The beamforming weight generation unit 1104 receives the second channel estimation value from the channel estimation value measurement unit 1103, and directs the transmission beam from the second system second base station 131 to the second system second mobile station 132. Generate forming weights. Beam forming weight generation section 1104 outputs the generated beam forming weight to weight combining section 1105.

The weight combining unit 1105 receives the null steering weight from the null steering weight generation unit 1102 and the beam forming weight from the beam forming weight generation unit 1104, and linearly combines the null steering weight and the beam forming weight. Here, assuming that the null steering weight vector, the beam forming vector, and the weighting coefficient are W _null , W _beam , and α, respectively, the weight vector W after weight synthesis is expressed by Equation (1).
W = αW _null + (1−α) W _beam (1)
W _null , W _beam , and W are “1 × number of transmitting antennas” row vectors.

  Here, when the weighting factor α is increased, priority is given to the reduction of interference with the second system first base station 121, and when the weighting factor α is reduced, the weight vector giving priority to the increase of the signal power to the second system second mobile station 132 is obtained. Generated. Note that the weighting factor α is, for example, a ratio of received signal power to interference noise power with mobile stations under the second system first base station 121 and second system second base station 132: SINR (Signal to Interference plus Noise Power Ratio). ), Determined based on communication load, positional relationship, etc.

  As a specific example of determining the weighting factor α, a method for determining to satisfy the required reception SINR of the second system first base station 121 or a determination to satisfy the required reception SINR of the second system second mobile station 132 is possible. The method of doing is mentioned. Further, there is a method of determining the weighting factor α based on a standard that maximizes the total communication capacity of the cells under the second system first base station 121 and the cells under the second system second base station 131. As another example, when the communication load of the second system first base station 121 is small, the weighting factor α is decreased, and when the communication load of the second system first base station 121 is large, the weighting factor α is increased. The method of doing is mentioned. Similarly, when the communication load on the second system second mobile station 132 is small, the weighting factor α is increased, and when the communication load on the second system second mobile station 132 is large, there is a method of decreasing the weighting factor α. Can be mentioned.

  FIG. 12 is a flowchart showing a series of operation examples in which the second system second base station 131 performs null steering and beamforming operations.

  Steps B01 to B03 perform the same processing as steps A01 to A03 in FIG. Hereinafter, step B04 and subsequent steps will be described.

  The second system second mobile station 132 performs uplink transmission to the second system second base station 131 (step B04).

  The second system second base station 131 receives the pilot signal transmitted from the second system second mobile station 132, and receives the second signal between the second system second mobile station 132 and the second system first base station 131. A channel estimation value is acquired (step B05).

  The second system second base station 131 combines the null steering weight and the beamforming weight (step B06).

  The second system second base station 131 applies the null steering and the beam forming using the combined weight and performs downlink transmission (step B07).

  FIG. 13 is a configuration diagram showing a use state of radio resources at a use frequency when step B07 in the flowchart of FIG. 12 is executed. FIG. 13A shows the use status of the radio resources of the cells under the second system first base station 121, and FIG. 13B shows the use status of the radio resources of the cells under the second system second base station 131. In the cell under the second system second base station 132 in FIG. 13 (b), downlink transmission is performed using a weight obtained by combining the null steering weight and the beamforming weight in the t2 slot.

  FIG. 14 is a schematic diagram showing inter-base station interference when step B07 in the flowchart of FIG. 12 is executed. In the third embodiment, in the t2 slot, the second system second base station 131 applies null steering to the second system first base station 121 and at the same time applies to the second system second mobile station 132. Apply beamforming to direct the directivity of the transmit beam.

  With the configuration and operation described above, in the third embodiment of the present invention, it is possible to achieve both reduction in interference with the second system first base station 121 and increase in signal power with respect to the second system second mobile station 132.

  In the first to third embodiments of the present invention, the example in which the first system and the second system share the frequency has been described. However, the present invention may be applied to a general TDD system in which the second system does not share the frequency. it can.

  In the first to third embodiments, one second system base station is arranged inside the second system base station transmission boundary 1502 and one second system is arranged outside the second system base station transmission boundary 1502. Although an example in which a base station is arranged has been described, a plurality of second system base stations are arranged inside the second system base station transmission boundary 1502, and a plurality of second system base stations are arranged outside the second system base station transmission boundary 1502. The present invention can also be applied to an example in which a two-system base station is arranged to reduce interference between the second systems.

  In the third embodiment, an example in which the channel estimation value is fed back from the second system first base station 121 to the second system second base station 131 via the inter-base station interface 141 has been described. The present invention can also be applied to an example in which PMI is fed back instead of the estimated value.

  Further, in the first to third embodiments, an example is given in which the second system first base station 121 and the second system second base station 131 feed back a channel estimation value or PMI via the inter-base station interface 141. As described above, the present invention may be applied when the base station is a remote radio head and the inter-base station interface 141 is an interface in the same device.

  In addition, the first to third embodiments described above can be embodied as predetermined hardware, for example, a circuit.

  The first to third embodiments described above can be controlled and operated by a computer circuit (for example, a CPU (Central Processing Unit)) (not shown) based on a control program. In this case, these control programs are stored in a wireless receiver or a storage medium inside the baseband unit (for example, a ROM (Read Only Memory) or a hard disk) or an external storage medium (for example, a removable medium or a removable disk). And read and executed by the computer circuit.

  The present invention can be suitably applied as long as it is a technology of a wireless communication system in which a plurality of base stations use the same frequency.

(Appendix 1)
A wireless communication system in which a plurality of base stations use the same frequency,
Measuring means for measuring a channel estimate between the first base station and the interfering second base station at the interfered first base station;
Multiplication means for multiplying a downlink transmission signal by a transmission weight according to the measured channel estimation value;
A wireless communication system, comprising: transmission means for transmitting the multiplied transmission signal from the second base station.

(Appendix 2)
The wireless communication system according to supplementary note 1, wherein the first base station is arranged closer to a base station of the existing wireless communication system than the second base station.

(Appendix 3)
The uplink and downlink time slot assignments are different between the first and second base stations, and the first and second base stations are located at positions where interference occurs between the first and second base stations. The wireless communication system according to Supplementary Note 1 or Supplementary Note 2, wherein the wireless communication system is arranged.

(Appendix 4)
The transmission weight is generated by using the measured channel estimation value so that interference from the second base station to the first base station is reduced. A wireless communication system according to any one of the above.

(Appendix 5)
The transmission weight is a transmission weight corresponding to a transmission weight index selected according to the measured channel estimation value from a codebook storing predetermined transmission weight candidates. The wireless communication system according to any one of 1 to Appendix 3.

(Appendix 6)
The transmission weight is a null steering weight generated using the measured channel estimation value so that interference from the second base station to the first base station is reduced.
The beamforming weight generated so that the received signal power at the mobile station under the second base station is increased using the channel estimation value between the mobile station under the second base station and the second base station. The wireless communication system according to any one of Supplementary Note 1 to Supplementary Note 3, wherein the transmission weights are combined according to a weighting factor.

(Appendix 7)
The weighting factor is determined according to at least one parameter of a received signal power to interference noise power ratio, a communication load, and a positional relationship of mobile stations under the first base station and the second base station. The wireless communication system according to attachment 6.

(Appendix 8)
A base station of a wireless communication system in which a plurality of base stations use the same frequency,
The downlink transmission signal is multiplied by a transmission weight measured by the first base station on the interfered side and according to a channel estimation value between the first base station and the second base station on the interfering side. Multiplication means;
A base station comprising: transmission means for transmitting the multiplied transmission signal from the second base station.

(Appendix 9)
The base station according to appendix 8, wherein the first base station is arranged near a base station of the existing wireless communication system as compared with the second base station.

(Appendix 10)
The uplink and downlink time slot assignments are different between the first and second base stations, and the first and second base stations are located at positions where interference occurs between the first and second base stations. The base station according to appendix 8 or appendix 9, wherein the base station is arranged.

(Appendix 11)
The transmission weight is generated using the measured channel estimation value so that interference from the second base station to the first base station is reduced. Base station in any one of.

(Appendix 12)
The transmission weight is a transmission weight corresponding to a transmission weight index selected according to the measured channel estimation value from a codebook storing predetermined transmission weight candidates. The base station according to any one of 8 to appendix 10.

(Appendix 13)
The transmission weight is a null steering weight generated using the measured channel estimation value so that interference from the second base station to the first base station is reduced.
The beamforming weight generated so that the received signal power at the mobile station under the second base station is increased using the channel estimation value between the mobile station under the second base station and the second base station. The base station according to any one of appendix 8 to appendix 10, wherein the transmission weights are combined according to a weighting factor.

(Appendix 14)
The weighting factor is determined according to at least one parameter of a received signal power to interference noise power ratio, a communication load, and a positional relationship of mobile stations under the first base station and the second base station. The base station according to attachment 13.

(Appendix 15)
A transmission method of a wireless communication system in which a plurality of base stations use the same frequency,
A measurement step of measuring, at the first base station, a channel estimation value between the interfered first base station and the interfered second base station;
A multiplication step of multiplying a downlink transmission signal by a transmission weight according to the measured channel estimation value;
And a transmission step of transmitting the multiplied transmission signal from the second base station.

(Appendix 16)
The transmission method according to supplementary note 15, wherein the first base station is arranged closer to a base station of the existing wireless communication system than the second base station.

(Appendix 17)
The uplink and downlink time slot assignments are different between the first and second base stations, and the first and second base stations are located at positions where interference occurs between the first and second base stations. The transmission method according to supplementary note 15 or supplementary note 16, wherein the transmission method is arranged.

(Appendix 18)
The transmission weight is generated using the measured channel estimation value so that interference from the second base station to the first base station is reduced. The transmission method according to any one of the above.

(Appendix 19)
The transmission weight is a transmission weight corresponding to a transmission weight index selected according to the measured channel estimation value from a codebook storing predetermined transmission weight candidates. The transmission method according to any one of 15 to appendix 17.

(Appendix 20)
The transmission weight is a null steering weight generated using the measured channel estimation value so that interference from the second base station to the first base station is reduced.
The beamforming weight generated so that the received signal power at the mobile station under the second base station is increased using the channel estimation value between the mobile station under the second base station and the second base station. The transmission method according to any one of supplementary note 15 to supplementary note 17, wherein the transmission weights are combined according to a weighting factor.

(Appendix 21)
The weighting factor is determined according to at least one parameter of a received signal power to interference noise power ratio, a communication load, and a positional relationship of mobile stations under the first base station and the second base station. The transmission method according to attachment 20.

(Appendix 22)
A base station program in a wireless communication system in which a plurality of base stations use the same frequency, the program
The downlink transmission signal is multiplied by a transmission weight measured by the first base station on the interfered side and according to a channel estimation value between the first base station and the second base station on the interfering side. Multiplication means;
A program that causes the multiplied transmission signal to function as a transmission unit that transmits from the second base station.

(Appendix 23)
The program according to appendix 22, wherein the first base station is arranged closer to a base station of the existing wireless communication system than the second base station.

(Appendix 24)
The uplink and downlink time slot assignments are different between the first and second base stations, and the first and second base stations are located at positions where interference occurs between the first and second base stations. 24. The program according to appendix 22 or appendix 23, wherein the program is arranged.

(Appendix 25)
The transmission weight is generated using the measured channel estimation value so that interference from the second base station to the first base station is reduced. A program according to any of the above.

(Appendix 26)
The transmission weight is a transmission weight corresponding to a transmission weight index selected according to the measured channel estimation value from a codebook storing predetermined transmission weight candidates. The program according to any one of 22 to appendix 24.

(Appendix 27)
The transmission weight is a null steering weight generated using the measured channel estimation value so that interference from the second base station to the first base station is reduced.
The beamforming weight generated so that the received signal power at the mobile station under the second base station is increased using the channel estimation value between the mobile station under the second base station and the second base station. 25. The program according to any one of Supplementary Note 22 to Supplementary Note 24, wherein the transmission weights are synthesized according to a weighting factor.

(Appendix 28)
The weighting factor is determined according to at least one parameter of a received signal power to interference noise power ratio, a communication load, and a positional relationship of mobile stations under the first base station and the second base station. The base station according to attachment 27.

111 First System Base Station 121 Second System First Base Station 122 Second System First Mobile Station 131 Second System Second Base Station 132 Second System Second Mobile Station 141 Inter-Base Station Interface 301 Channel Estimate Measurement Unit 302 Channel estimation value notification unit 401 Channel estimation value acquisition unit 402 Null steering weight generation unit 403 Downlink transmission signal generation unit 404 Multiplication unit 405 RF transmission unit 901 Codebook holding unit 902 PMI selection unit 903 PMI notification unit 1001 PMI acquisition unit 1002 Null steering Weight generation unit 1101 Channel estimation value acquisition unit 1102 Null steering weight generation unit 1103 Channel estimation value measurement unit 1104 Beamforming weight generation unit 1105 Weight synthesis unit 1501 First system protection boundary 1502 Second system Base station transmission boundary 1511 first system radio 1521 second system first base station 1522 second system first mobile station 1531 second system second base station 1532 second system second mobile station

Claims (8)

A wireless communication system in which a plurality of base stations use the same frequency,
Measuring means for measuring a channel estimate between the first base station and the interfering second base station at the interfered first base station;
Multiplication means for multiplying a downlink transmission signal by a transmission weight according to the measured channel estimation value;
Transmitting means for transmitting the multiplied transmission signal from the second base station ,
The uplink and downlink time slot assignments are different between the first and second base stations,
The first base station is disposed in the vicinity of a base station of an existing wireless communication system, compared to the second base station,
The wireless communication system , wherein the first and second base stations are arranged at a position where interference occurs between the first and second base stations .   The transmission weight is generated using the measured channel estimation value so as to reduce interference from the second base station to the first base station. Wireless communication system.   The transmission weight is a transmission weight corresponding to a transmission weight index selected according to the measured channel estimation value from a codebook storing predetermined transmission weight candidates. Item 2. The wireless communication system according to Item 1. The transmission weight is a null steering weight generated using the measured channel estimation value so that interference from the second base station to the first base station is reduced.
The beamforming weight generated so that the received signal power at the mobile station under the second base station is increased using the channel estimation value between the mobile station under the second base station and the second base station. The wireless communication system according to claim 1, wherein the transmission weights are combined according to a weighting factor. The weighting factor is determined according to at least one parameter of a received signal power to interference noise power ratio, a communication load, and a positional relationship of mobile stations under the first base station and the second base station. The wireless communication system according to claim 4 . A base station of a wireless communication system in which a plurality of base stations use the same frequency,
The downlink transmission signal is multiplied by a transmission weight measured by the first base station on the interfered side and according to a channel estimation value between the first base station and the second base station on the interfering side. Multiplication means;
Transmitting means for transmitting the multiplied transmission signal from the second base station ,
The uplink and downlink time slot assignments are different between the first and second base stations,
The first base station is disposed in the vicinity of a base station of an existing wireless communication system, compared to the second base station,
The base station, wherein the first and second base stations are arranged at a position where interference occurs between the first and second base stations. A transmission method of a wireless communication system in which a plurality of base stations use the same frequency,
A measurement step of measuring, at the first base station, a channel estimation value between the interfered first base station and the interfered second base station;
A multiplication step of multiplying a downlink transmission signal by a transmission weight according to the measured channel estimation value;
Transmitting the multiplied transmission signal from the second base station ,
The uplink and downlink time slot assignments are different between the first and second base stations,
The first base station is disposed in the vicinity of a base station of an existing wireless communication system, compared to the second base station,
The transmission method according to claim 1, wherein the first and second base stations are arranged at a position where interference occurs between the first and second base stations . A base station program in a wireless communication system in which a plurality of base stations use the same frequency, the program
The downlink transmission signal is multiplied by a transmission weight measured by the first base station on the interfered side and according to a channel estimation value between the first base station and the second base station on the interfering side. Multiplication means;
Function as transmission means for transmitting the multiplied transmission signal from the second base station ;
The uplink and downlink time slot assignments are different between the first and second base stations,
The first base station is disposed in the vicinity of a base station of an existing wireless communication system, compared to the second base station,
The program according to claim 1, wherein the first and second base stations are arranged at a position where interference occurs between the first and second base stations .

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